This invention relates to humidity sensitive devices and more particularly to a humidity sensitive device comprised of a magnesium aluminate spinel and a titania material.
Humidity sensitive devices are used in various applications to measure the humidity of atmospheric environments. The measured humidity may be used to control the operation of a process being performed. An example of a humidity controlled process is the microwave cooking of a food substance in which the heating cycle is dependent on the measured humidity within the microwave oven. Such a humidity controlled microwave oven is described, for example, in U.S. Pat. No. 4,080,564 issued to T. Nitta et al., Mar. 21, 1978. Also described in U.S. Pat. No. 4,080,564 is the use of radiant heat to periodically purge the humidity sensor of foreign substances, such as oil, that may be deposited on the sensor during the microwave heating of the food substance. The foreign substance may interfere with the humidity sensing characteristics of the device.
It is also known that humidity sensitive devices may be used in air conditioning apparatus and also heating apparatus. The air conditioner apparatus may sense the humidity as an indication to determine when moisture should be removed from the environment in order to provide a more pleasantly cooled environment. Conversely, a heating apparatus may sense the humidity as an indication to determine when moisture should be added to the environment in order to provide a more pleasantly warmed environment.
In the above-given applications of humidity sensitive devices it is desirable that the humidity sensor provide an accurate measurement of the humidity. Also, it is desirable that the humidity sensitive devices provide repeatability, that is, the same measurement of humidity be provided under similar conditions over a periodic time.
Repeatability is hindered when the characteristics of the humidity sensitive material, such as a metal oxide, change or drift over a period of time. The material characteristics of the metal oxides may be restored or rejuvenated by the application of heat to elevate the material to a relatively high temperature in the order of 400.degree. C. If a humidity sensitive material requires frequent rejuvenation to maintain repeatability, the required rejuvenation may interfere with the desired heating or cooling process being performed.
Accordingly, an object of the present invention is to provide a humidity sensitive device that provides an accurate measurement of the humidity and requires relatively infrequent rejuvenation.
A further object of the present invention is to provide a humidity sensitive device having various means for applying heat for rejuvenation.
A still further object of the present invention is to provide a low cost, endurable and accurate device that may be used in various atmospheric environments, such as, microwave ovens, air conditioners, and heating apparatus to measure humidity.
These and other objects of this invention will become apparent upon consideration of the following detailed description taken together with the accompanying drawings.